We consider the issue of the top quark Yukawa coupling measurement in a model-independent and general case with the inclusion of $CP$ violation in the coupling. Arguably the best process to study this coupling is the associated production of the Higgs boson along with a $t\overline{t}$ pair in a machine like the International Linear Collider (ILC). While detailed analyses of the sensitivity of the measurement—assuming a Standard Model (SM)-like coupling is available in the context of the ILC—conclude that the coupling could be pinned down to about a 10% level with modest luminosity, our investigations show that the scenario could be different in the case of a more general coupling. The modified Lorentz structure resulting in a changed functional dependence of the cross section on the coupling, along with the difference in the cross section itself leads to considerable deviation in the sensitivity. Our studies of the ILC with center-of-mass energies of 500 GeV, 800 GeV, and 1000 GeV show that moderate $CP$ mixing in the Higgs sector could change the sensitivity to about 20%, while it could be worsened to 75% in cases which could accommodate more dramatic changes in the coupling. Detailed considerations of the decay distributions point to a need for a relook at the analysis strategy followed for the case of the SM, such as for a model-independent analysis of the top quark Yukawa coupling measurement. This study strongly suggests that a joint analysis of the $CP$ properties and the Yukawa coupling measurement would be the way forward at the ILC and that caution must be exercised in the measurement of the Yukawa couplings and the conclusions drawn from it.

There have been some recent claims in the literature about large right-handed sneutrinos contributions to lepton flavor violating observables like $\mu \to 3e$ or $\mu -e$ conversion in nuclei in supersymmetric low-scale seesaw models. These large contributions originate from $Z$-penguin diagrams which show a much weaker dependence on the heavy masses than the photonic contributions. We have traced this to an error in the evaluation of the corresponding loop amplitudes which has propagated in the literature. We explicitly show that after correcting this mistake the $Z$-penguins show the expected decoupling behavior. Moreover, the reported dominance of the $Z$-penguin over the photonic contributions disappears as well.

We analyze a scenario in which the lightest heavy neutrino $N_1$ is a dark matter candidate and the second-heaviest neutrino $N_2$ decays producing a lepton number. If $N_1$ were in thermal equilibrium, its energy density today would be much larger than that of the observed dark matter, so we consider energy injection by the decay of $N_2$. In this paper, we show the parameters of this scenario that give the correct abundances of dark matter and baryonic matter and also induce the observed neutrino masses. This model can explain a possible sterile neutrino dark matter signal of $M_1=7\mathrm{keV}$ in the x-ray observation of x-ray multi-mirror mission.

We extend the general formalism of two-photon exchange to elastic lepton-nucleon scattering by accounting for all lepton mass terms. We then perform a numerical estimate of the muon-proton scattering at low momentum transfer in view of the future MUSE experiment. For this purpose, we estimate the two-photon exchange corrections to muon-proton scattering observables by considering the contribution of the proton intermediate state, which is expected to dominate at very low momentum transfers. We find that the two-photon exchange effect to the unpolarized muon-proton scattering cross section in the MUSE kinematical region is of the order of 0.5%.

A search is presented for production of dark-matter particles recoiling against a leptonically decaying $Z$ boson in $20.3{\mathrm{fb}}^{-1}$ of $pp$ collisions at $\sqrt{s}=8\mathrm{TeV}$ with the ATLAS detector at the Large Hadron Collider. Events with large missing transverse momentum and two oppositely charged electrons or muons consistent with the decay of a $Z$ boson are analyzed. No excess above the Standard Model prediction is observed. Limits are set on the mass scale of the contact interaction as a function of the dark-matter particle mass using an effective field theory description of the interaction of dark matter with quarks or with $Z$ bosons. Limits are also set on the coupling and mediator mass of a model in which the interaction is mediated by a scalar particle.

The resonant structure of the reaction ${\overline{B}}^0\to J/\psi {\pi }^{+}{\pi }^{-}$ is studied using data from $3{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the LHCb experiment, one third at 7 TeV center-of-mass energy and the remainder at 8 TeV. The invariant mass of the ${\pi }^{+}{\pi }^{-}$ pair and three decay angular distributions are used to determine the fractions of the resonant and nonresonant components. Six interfering ${\pi }^{+}{\pi }^{-}$ states, $\rho (770)$, $f_0(500)$, $f_2(1270)$, $\rho (1450)$, $\omega (782)$ and $\rho (1700)$, are required to give a good description of invariant mass spectra and decay angular distributions. The positive and negative charge parity fractions of each of the resonant final states are determined. The $f_0(980)$ meson is not seen and the upper limit on its presence, compared with the observed $f_0(500)$ rate, is inconsistent with a model where these scalar mesons are formed from two quarks and two antiquarks (tetraquarks) at the eight standard deviation level. In the $q\overline{q}$ model, the absolute value of the mixing angle between the $f_0(980)$ and the $f_0(500)$ scalar mesons is limited to be less than 17° at 90% confidence level.

Recently, BICEP2 found that the vanishing of the tensor-to-scalar ratio $r$ is excluded at $7\sigma$ level, and its most likely value is $r=0.2_{-0.05}^{+0.07}$. This immediately causes a tension with the Planck constraint $r<0.11$. In addition, it also implies that the inflaton (in single field slow-roll inflation) experienced a Planck excursion during inflation $\mathrm{\Delta }\varphi /M_{Pl}\ge \mathcal{O}(1)$, whereby the effective theory of inflation becomes questionable. In this brief report, we show that the inflationary paradigm is still robust, even after the quantum effects are taken into account. Moreover, these effects also help to relax the tension on the different values of $r$ given by BICEP2 and Planck.

In a recent paper, Schutz proposed an analytical approximation for simplifying the treatment of the polarization angle and conveniently evaluating relative detection rates of compact binary inspirals for various networks of ground-based interferometers. We derive relative event rates by strictly handling the polarization angle, and we quantitatively examine the validity of Schutz’s approximation. The associated error of the approximation is rigorously shown to be less than 1.02%, irrespective of the details of the detector networks.

We calculate the triple gluon, ghost-gluon and quark-gluon vertex functions at two loops in the $\overline{\mathrm{MS}}$ scheme in the chiral limit for an arbitrary linear covariant gauge when the external legs are all off shell.

Recent work by Cachazo et al.arXiv:1309.0885 shows that connected prescription residues obey the global identities of $\mathcal{N}=4$ super-Yang-Mills amplitudes. In particular, they obey the Bern-Carrasco-Johansson (BCJ) amplitude identities. Here we offer a new way of interpreting this result via objects that we call residue numerators. These objects behave like the kinematic numerators introduced by BCJ except that they are associated with individual residues. In particular, these new objects satisfy a double-copy formula relating them to the residues appearing in recently discovered analogs of the connected prescription integrals for $\mathcal{N}=8$ supergravity. Along the way, we show that the BCJ amplitude identities are equivalent to the consistency condition that allows kinematic numerators to be expressed as amplitudes using a generalized inverse.

We develop a waveform model to describe the inspiral, merger and ringdown of binary systems with comparable and intermediate mass ratios. This model incorporates first-order conservative self-force corrections to the energy and angular momentum, which are valid in the strong-field regime [S. Akcay et al., Phys. Rev. D 86, 104041 (2012)]. We model the radiative part of the self-force by deriving second-order radiative corrections to the energy flux. These corrections are obtained by minimizing the phase discrepancy between our self-force model and the effective one body model [Y. Pan et al., Phys. Rev. D 84, 124052 (2011) and T. Damour et al., Phys. Rev. D 87, 084035 (2013)] for a variety of mass ratios. We show that our model performs substantially better than post-Newtonian approximants currently used to model neutron star–black hole mergers from early inspiral to the innermost stable circular orbit. In order to match the late inspiral evolution onto the plunge regime, we extend the “transition phase” developed by Ori and Thorne Phys. Rev. D 62, 124022 (2000) by including finite mass-ratio corrections and modeling the orbital phase evolution using an implicit rotating source [J. G. Baker et al., Phys. Rev. D 78, 044046 (2008)]. We explicitly show that the implicit rotating source approach provides a natural transition from late-time radiation to ringdown that is equivalent to ringdown waveform modeling based on a sum of quasinormal modes.

The generalized uncertainty principle (GUP) corrected modified relativistic particle model has been derived in curved space-time. From this modified model, the equation of motion (EM) has been constructed relativistically in terms of the affine parameter ($\lambda$) or proper time ($\tau$) and nonrelativistically in terms of coordinate time ($t$). In this context, the constraint analysis technique has been applied to get the EM. Interestingly, the EM obtained in both cases is the usual one. This result clearly indicates an important fact, that is, consistency of the equivalence principle in the GUP framework, and furthermore it can be concluded that with the GUP-corrected modified algebra it is impossible to get the GUP effect in point particle motion.

We reconsider the entropic-force model in which both kinds of Hubble terms, $\dot{H}$ and $H^2$, appear in the effective dark energy (DE) density affecting the evolution of the main cosmological functions, namely, the scale factor, deceleration parameter, matter density, and growth of linear matter perturbations. However, we find that the entropic-force model is not viable at the background and perturbation levels due to the fact that the entropic formulation does not add a constant term in the Friedmann equations. On the other hand, if on mere phenomenological grounds we replace the $\dot{H}$ dependence of the effective DE density with a linear term $H$ without including a constant additive term, we find that the transition from deceleration to acceleration becomes possible, but the recent structure formation data strongly disfavor this cosmological scenario. Finally, we briefly compare the entropic-force models with some related DE models (based on dynamical vacuum energy) which overcome these difficulties and are compatible with the present observations.

We propose a model based on the $SU(5)$ grand unification with an extra $A_4\otimes Z_2\otimes Z_2^{\prime }\otimes Z_2^{\prime \prime }\otimes U{(1)}_f$ flavor symmetry, which accounts for the pattern of the SM fermion masses and mixings. The observed hierarchy of charged fermion masses and quark mixing matrix elements arises from a generalized Froggatt-Nielsen mechanism triggered by a scalar $\mathbf{24}$ representation of $SU(5)$ charged under the global $U(1{)}_f$ and acquiring a VEV at the GUT scale. The light neutrino masses are generated via a radiative seesaw mechanism with a single heavy Majorana neutrino and neutral scalars running in the loops. The model predictions for both quark and lepton sectors are in good agreement with the experimental data. The model predicts an effective Majorana neutrino mass, relevant for neutrinoless double beta decay, with values $m_{\beta \beta }=4$ and 50 meV for the normal and the inverted neutrino spectrum, respectively. The model also features a suppression of $CP$ violation in neutrino oscillations, a low scale for the heavy Majorana neutrino (few TeV) and, due to the unbroken $Z_2$ symmetry, a natural dark matter candidate.

The purpose of this paper is twofold. The first purpose is to find a fully Poincaré invariant solution of the Bethe-Salpeter equation (BSE) for excited quarkonia; however, the second, in fact, major focus is on the relevance of the space-time metric choice and its impact on the correct description of the ground and all excited states. For the first time, we compare the BSE solutions defined independently with the Euclidean and Minkowski metric. For this purpose, the BSE is conventionally defined and solved in Euclidean space with two versions of the propagator: the bare propagator and the confined form of the quark propagator with complex conjugated poles. In both considered cases, there is unexpected doubling of the spectrum when comparing to the experiments as well as to the solutions of the Schrödinger equation. The quark propagator with complex conjugated singularities allows us to find the BSE solution directly in Minkowski momentum space as well. We find the Minkowski space solution for confining theories is not only numerically accessible but provides a reliable albeit not yet completely satisfactory description of the ground and excited meson states.

We study the pion leading-twist distribution amplitude (DA) within the framework of Shifman-Vainshtein-Zakharov sum rules under the background field theory. To improve the accuracy of the sum rules, we expand both the quark propagator and the vertex $(z·\overleftrightarrow{D}{)}^n$ of the correlator up to dimension-six operators in the background field theory. The sum rules for the pion DA moments are obtained, in which all condensates up to dimension-six have been taken into consideration. Using the sum rules, we obtain $⟨{\xi }^2⟩{|}_{1\mathrm{GeV}}=0.338\pm 0.032$, $⟨{\xi }^4⟩{|}_{1\mathrm{GeV}}=0.211\pm 0.030$ and $⟨{\xi }^6⟩{|}_{1\mathrm{GeV}}=0.163\pm 0.030$. It is shown that the dimension-six condensates shall provide sizable contributions to the pion DA moments. We show that the first Gegenbauer moment of the pion leading-twist DA is $a_2^{\pi }{|}_{1\mathrm{GeV}}=0.403\pm 0.093$, which is consistent with those obtained in the literature within errors but prefers a larger central value as indicated by lattice QCD predictions.

The search for additional Higgs particles and the exact measurements of Higgs (self-)couplings is a major goal of future collider experiments. In this paper we investigate the possible sizes of new physics signals in these searches in the context of the $CP$-conserving two-Higgs-doublet model (2HDM) of type II. Using current constraints from flavor, electroweak precision, and Higgs signal strength data, we determine the allowed sizes of the triple-Higgs couplings and the branching fractions of the heavy Higgs bosons into lighter Higgs bosons. Identifying the observed Higgs resonance with the light $CP$-even 2HDM Higgs boson $h$, we find that the $hhh$ coupling cannot exceed its Standard Model (SM) value, but can be reduced by a factor of 0.56 at the $2\sigma$ level. The branching fractions of the heavy neutral Higgs bosons $H$ and $A$ into two-fermion or two-vector-boson final states can be reduced by factors of 0.4 and 0.01, respectively, if decays into a lighter Higgs boson are possible and if the mass of the decaying Higgs is below the $t\overline{t}$ threshold. To facilitate future studies of collider signatures in 2HDM scenarios with large triple-Higgs couplings or decay modes of the heavy Higgs bosons not covered by the SM Higgs searches we provide a set of benchmark points which exhibit these features and agree with all current constraints. We also discuss the effect of the heavy Higgs bosons on the $gg\to hh$ cross section at a 14 TeV LHC for some of these benchmarks. For $m_H$ below the $hh$ threshold we see a reduction of the SM $gg\to hh$ cross section due to destructive interference, but for $m_H$ above the $hh$ threshold current constraints allow enhancement factors above 50. An enhancement factor of 6 is still possible in scenarios in which the heavy Higgs particles would not be discovered by standard searches after $300{\mathrm{fb}}^{-1}$ of data.

We study the most general scalar potential of the Georgi-Machacek model, which adds isospin-triplet scalars to the Standard Model (SM) in a way that preserves custodial SU(2) symmetry. We show that this model possesses a decoupling limit, in which the predominantly-triplet states become heavy and degenerate while the couplings of the remaining light neutral scalar approach those of the SM Higgs boson. We find that the SM-like Higgs boson couplings to fermion pairs and gauge boson pairs can deviate from their SM values by corrections as large as $\mathcal{O}(v^2/M_{\text{new}}^2)$, where $v$ is the SM Higgs vacuum expectation value and $M_{\text{new}}$ is the mass scale of the predominantly-triplet states. In particular, the SM-like Higgs boson couplings to $W$ and $Z$ boson pairs can decouple much more slowly than in two Higgs doublet models, in which they deviate from their SM values like $\mathcal{O}(v^4/M_{\text{new}}^4)$. Furthermore, near the decoupling limit the SM-like Higgs boson couplings to $W$ and $Z$ pairs are always larger than their SM values, which cannot occur in two Higgs doublet models. As such, a precision measurement of Higgs couplings to $W$ and $Z$ pairs may provide an effective method of distinguishing the Georgi-Machacek model from two Higgs doublet models. Using numerical scans, we show that the coupling deviations can reach 10% for $M_{\text{new}}$ as large as 800 GeV.

We present a novel technique for the determination of the topological susceptibility (related to the variance of the distribution of global topological charge) from lattice gauge theory simulations, based on maximum-likelihood analysis of the Markov-chain Monte Carlo time series. This technique is expected to be particularly useful in situations where relatively few tunneling events are observed. Restriction to a lattice subvolume on which topological charge is not quantized is explored, and may lead to further improvement when the global topology is poorly sampled. We test our proposed method on a set of lattice data, and compare it to traditional methods.

In the present work we explore the production potential of ${\mathrm{\Lambda }}_c(2880{)}^{+}$ at PANDA. With the $J^P={\frac{5}{2}}^{+}$ assignment to ${\mathrm{\Lambda }}_c(2880{)}^{+}$, we calculate the differential and total cross sections of $p\overline{p}\to {\mathrm{\Lambda }}_c^{-}{\mathrm{\Lambda }}_c(2880{)}^{+}$. We also perform the Dalitz plot analysis and give the $p{D}^0$ invariant mass spectrum distribution of the process $p\overline{p}\to {\mathrm{\Lambda }}_c^{-}p{D}^0$, where the signal and background contributions are considered. Our numerical results indicate that the production of ${\mathrm{\Lambda }}_c(2880{)}^{+}$ may reach up to about $20\mu \mathrm{b}$. About ${10}^7$ events from the reconstruction of $p{D}^0$ can be accumulated per day, if taking the designed luminosity ($2\times {10}^{32}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$) of PANDA.